1. Field of the Invention
The present invention relates generally to a non-reciprocating engine of the rotary variety in which a multiplicity of pistons are used to provide motive power.
2. Description of the Prior Art
Historically, engines relying on the Otto cycle, Diesel cycle or other thermodynamic cycles have been constructed in two general classes: reciprocating and rotary.
Reciprocating engines are characterized by translational movement of power producing elements. The power producing elements most commonly consist of one or more pistons, each of which are in the shape of a cylindrical section. One end of the piston is a flat surface and the other is connected to a lever arm which, in turn, is connected to a crankshaft. The pistons are constrained to move within a hollow cylindrical shaft along their common axis. Typically, one end of the cylinder is closed and the flat end of the piston is positioned facing this closed end. In an internal combustion embodiment of the reciprocating engine, valved ports passing through or near the closed end of the cylinder provide a means to permit fluids to pass in and out of the cylinder. The input fluids commonly are comprised of a hydrocarbon fuel and ambient air to facilitate the combustion of the fuel.
In an internal combustion embodiment, fuel and air are introduced through the valved ports into the cylinder and the piston is driven toward the closed end of the cylinder, thereby pressurizing the fuel and air. Power is produced by first detonating the fuel-air mixture. The force produced by the resulting combustion, constrained by the immovable walls of the cylinder, is channeled against the piston, propelling it toward the open end of the cylinder. As a result, the lever arm exerts force on the crankshaft, ultimately providing torque. Through the action of other cylinders and their operative interconnection with the crankshaft, the piston is forced back into the cylinder and the process is repeated to produce continuous motion and torque.
Rotary engines are characterized by rotational motion of the power producing element about the central shaft of the engine. Typical, Wankel-type rotary engines employ pistons, commonly referred to as rotors, which orbit eccentrically about the central shaft of the engine within a chamber. The piston itself is roughly triangularly-shaped, with rounded, convex sides. The vertices of the triangle are capped with seals which maintain contact with the walls of the chamber. The chamber typically has a trochoidal cross-sectional shape. The seals on the piston divide the inside of the chamber into separate regions, each bounded by the walls of the chamber and one face of the piston. The inner volume of the piston has an inwardfacing gear with a larger diameter than the central shaft of the engine. The central shaft has an outward-facing gear enmeshed with the inward-facing gears of the pistons.
In an internal combustion rotary engine, power is produced as a result of combustive force sequentially applied to individual faces of the piston, forcing continuous orbiting of the piston. Four phases take place, generally three of the phases taking place simultaneously: intake/expansion, compression, ignition and exhaust. As the piston orbits, a first piston face will sweep past an intake vent, the orbit of the piston causing the region bounded by the first piston face and the chamber to expand, causing the pressure within the corresponding region of the chamber to be less than that outside the chamber, drawing in ambient air and/or fuel. At the same time, a second, adjacent piston face has just completed intake and the seal at the vertex between the first and second faces now has sealed off this region from the intake vent. The orbit of the rotor causes this second face to move toward the chamber wall, compressing the intake gases, usually air, and fuel. Once this region has been compressed to its minimum volume, the fuel-air mixture contained therein is ignited and the force of the combustion drives this second piston face away from the chamber wall. As a result, the gears on the inside of the piston exert force against the gears on the central axle of the engine, generating torque. The third piston face, having just completed its expansion phase, now sweeps past an output vent. The combustion-generated expansion of the second face causes this third face to be forced against the side of the chamber having the output vent, forcing spent combustion fluids out of the chamber. Once this expulsion is completed, the seal at the vertex between the second and third faces causes this third region to be closed from the output vent just as the region bounded by this third face now opens onto the intake vent, and the cycle begins anew with each 120 degree rotation of the piston.
Both the typical reciprocating and rotating engines suffer from various inefficiencies and methodological defects. The reciprocating engine suffers primarily from five such defects. First, the translational piston movement wastes the displacement capacity of the engine. Engine power is typically a function of its displacement, i.e.. the total volume bounded by the pistons and the cylinders at maximum expansion. In a typical four-cycle engine, for every two cycles of the engine, each piston only performs one power stroke. After a propulsive stroke (through 180 degrees of the engine's cycle), the piston's return stroke is used to expel waste gases from the propulsive stroke (through the remaining 180 degrees of the engine's cycle). In the next expansive stroke, through which the piston is pulled by the engine's crankshaft as the result of force generated by other cylinders, gases and fuel are drawn in for the next cycle and then compressed on the ensuing compressive stroke (requiring another 360 degrees of the engine's cycle). Then the cycle begins anew, once every 720 degrees. Thus, the typical four-cycle reciprocating engine is inefficient because each piston produces power only one fourth of the time.
Second, torque generation in a reciprocating engine is inefficient. The forces resulting from the combustion of fuels within the piston cylinders largely result in the application of stresses to various engine components rather than the production of useful work. As a result of the reciprocating engine's nature, force is exerted by the pistons orthogonally to the central axis of the engine. The greatest force is exerted upon the piston at maximum compression, when the force per unit volume of the detonated fluids is greatest. Unfortunately, it is at this point in the stroke, when the piston is farthest into the cylinder, where the piston's force is directed orthogonally against the shaft of the engine; it is at this point that the moment arm of the piston is at its shortest, thereby delivering the minimum torque per unit force. It is not until halfway through the stroke, when the combustive forces are substantially dissipated and exerting substantially less force on the piston, that the moment arm reaches is maximum length. Thus, in a reciprocating engine, the magnitude of the force has tremendously dissipated by the time the piston arm reaches a point where it is delivering the greatest torque per unit force.
Consequently, much of the force created in a reciprocating engine is wasted as structural stress. Since the greatest force in the reciprocating engine is created when the axis of the piston is perpendicular to the engine's crankshaft, tremendous sheer force is generated and directed against the engine's crankshaft. Further, when the moment arm is at a minimum, so is the rate of piston displacement. As a result, at detonation tremendous stress waves are applied to the chamber, the piston, and the piston rod. Because all the stresses are necessarily being applied at the worst possible time, engine parts must be carefully machined and relatively heavy to be able to withstand the unresolvable stresses.
Third, it should be noted that analogous waste takes place on the compressive stroke as the result of the minimum rate of piston displacement about the point of maximum compression. Because of the relatively slow movement of the piston at maximum compression resulting in relatively slow compression, as a matter of fluid mechanics, the pressurized gases have the greatest tendency to leak through seals between the piston and the chamber, wasting a portion of the engine's power.
Fourth, by their nature, reciprocating engines are necessarily complex. Because the pistons exert a propulsive stroke only once every two revolutions, valve means must be used to control the flow of fuel and combustion gases into and out of the chamber. Obviously, it would be wasteful for combustion gases and fuel to be passively drawn into the cylinder during the expulsive stroke. Accordingly, the valves, typically driven by cams, must be used to direct the engine. The valve means increase complexity, therefore increasing the risk of malfunction, and cost of such engines.
Fifth, it should be noted that the valves also reduce the efficiency of the engine by what commonly are termed breathing losses. The valves necessarily are relatively small because, practically, they must be made to fit within the piston cylinders without obstructing the motion of the pistons. Further, the valves open and close, alternately completely starting and stopping the flow of gases into the engine. Gases, like any other form of matter, create friction and possess inertia. There is fluid friction between the gases flowing through the limited valve openings. Further, periodically halting the flow of air into the mechanism means that it will take some period of time to reaccelerate the gases entering the chamber. As a result, because of the time it takes to reaccelerate the gases, less gas will be introduced into the piston chamber. Because there is less gas introduced into the chamber, the pressure will be reduced and the ultimate combustive force will be diminished.
Rotary engines also suffer from a number of problems, both in efficiency and in structural integrity. From an efficiency standpoint, the displacement and, therefore, the compression ratio, are relatively low, particularly as compared to the size of the piston and chamber. Thus, even though the piston can generate three force strokes per revolution, the strokes are not as powerful as those of a reciprocating engine.
Further, by definition, some of the force generated by the combustion of fluids in the engine is counterproductively applied. The rotary pistons actually straddle the axle to which the inward facing gear of the piston imparts power. Therefore, each face of the piston has a moment arm extending to both sides of the axle. Combustive force is applied to the entire face of the piston. As a result, while force is applied to a portion of the face acting as a positive moment arm to impart positive motion to the piston, force is also applied to the portion of the face straddling the axle on the other side, applying a negative moment to the axle. Thus, the positive torque generated by the rotary engine is partially offset by the inherent negative torque.
Additionally, to make up for the lack of displacement, rotary engines typically have to run faster, thereby running hotter, creating cooling and lubrication concerns. Further, because of the structure of the engine, tremendous stress is exerted not only on the gears of the inner surface of the piston and the engine shaft, but also on the seals at the vertices of the piston. If the seals do not effectively maintain the integrity of the separate regions, power is lost through dissipation, incompletely burned fuels are expelled resulting in emissions problems, and the intake phase does not work efficiently.
One must note both types of engines also suffer from the thermodynamic inefficiency caused by the cooling resulting from the delay between combustive power strokes. The cooling of the piston faces and chamber walls draw energy not only from the combustive phase but also, because of the direct relationship between pressure and temperature in a fixed volume, the pressure which can be generated is reduced in the compression phase of the engine.
The non-reciprocating engine of the present invention has been developed to overcome the deficiencies of prior art engines by generating torque with greater efficiency, reducing stress loading on critical elements and, generally, offering simplicity of design and manufacture.